1. Field of the Invention
The present invention relates to a method for producing a laminated dielectric, suitable for producing by low temperature firing a laminated dielectric having a low dielectric constant layer and a high dielectric constant layer alternately laminated so that a low dielectric constant layer constitutes the outer most layer, which is suitable for e.g. a substrate for a circuit or an antenna.
2. Discussion of Background
A small size substrate is used as a substrate for e.g. an antenna or a circuit for a small size electronic equipment such as a mobile phone to be used in a high frequency region such as a microwave range.
As such a small size substrate, a laminated dielectric substrate having a low dielectric constant layer, a high dielectric constant layer and a low dielectric constant layer laminated in this order, is known (e.g. JP-A-2001-284807).
The laminated dielectric substrate disclosed in the above publication, is prepared by laminating a glass ceramic composition to form a low dielectric constant layer and a magnesium titanate/glass-forming composition mixture to form a high dielectric constant layer and then cofiring them.
In the inner or on the surface of such a laminated dielectric substrate, a conductor composed mainly of silver or copper is usually formed. In such a case, it is common to apply or fill a silver paste or copper paste to form such a conductor at a desired portion, followed by the cofiring.
The high dielectric constant layer in the laminated dielectric disclosed in the above publication contains Li in each case. However, it is known that an alkali metal such as Li deteriorates the electrical insulating property. Further, in a case where a silver conductor is formed in contact with the high dielectric constant layer containing an alkali metal such as Li, migration of silver to such a layer is likely to take place to further deteriorate the electrical insulating property of the layer.
On the other hand, if cofiring is carried out as mentioned above, the fired object usually shrinks, and if the shrinkage is large, the dimensional precision of the laminated dielectric (the fired body) will deteriorate. However, with the laminated dielectric disclosed in the above publication, no such problem appears to be present. This is considered to be attributable to the fact that the high dielectric constant layer in the laminate is one obtainable by firing a mixture comprising a magnesium titanate and a small amount of a Li-containing glass-forming composition (its content represented by mass percentage being 27% at the maximum). Namely, it is considered that the shrinking behavior during the firing of the mixture having a small content of the Li-containing glass-forming composition is substantially different from the shrinking behavior of a glass ceramic composition (composed mainly of glass) to form a low dielectric constant layer, and the above-mentioned shrinkage is small.